This is a non-interventional cohort study evaluating non-relapse mortality and toxicities in patients with CTCL or ATLL treated with mogamulizumab pre- or post- alloHCT for patients transplanted beginning January 1, 2012 until accrual is complete.

This is an observational, retrospective and prospective study where subjects who have received mogamulizumab either within one year before or within 18 months after transplantation will be followed for data collection. Data will be collected at baseline (retrospectively), 100 days post alloHCT, 6-months, 1 year and at 2 years post alloHCT (retrospectively and prospectively).

A cut-off time limit of 18 months post alloHCT exposure will allow at least 6 months of follow-up within the 2 years post-alloHCT follow-up period.

Inclusion Criteria:

• Patients registered to the Center for International Blood and Marrow Transplant Research (CIBMTR)
• Adults ≥18 years of age with either CTCL or ATLL;
• AlloHCT performed from January 2012 onward.

Exclusion Criteria:

• Patients without consent for research.

The study population will include a minimum of 50 patients with CTCL or ATLL who received mogamulizumab within one year prior to alloHCT. At least 40 patients should have been diagnosed with CTCL and at least 33 patients should have received mogamulizumab as last therapy line before alloHCT. Data will be collected from no more than 100 controls with similar characteristics to the mogamulizumab-treated patients, and who have undergone alloHCT without exposure to mogamulizumab pre- or post-alloHCT. Information on patients receiving mogamulizumab within 18 months after alloHCT will also be collected.